Microcavity plasma devices have been developed and advanced by researchers at the University of Illinois, including inventors of this application. One segment of this research has resulted in microcavity plasma devices and arrays of microcavity plasma devices fabricated in semiconductor materials. Particular microcavity plasma devices having tapered sidewall microcavities fabricated in semiconductor materials are disclosed in U.S. Pat. No. 7,112,918 (the '918 patent), issued on Sep. 26, 2006 and entitled Microdischarge Devices and Arrays Having Tapered Microcavities.
The '918 patent describes microdischarge devices and arrays of microdischarge devices that have tapered cavities. The tapered cavities include pyramidal cavities, and are relatively inexpensive and easy to fabricate using conventional semiconductor processing techniques. Tailoring of the electrical properties of the microcavity devices by variation of the tapered microcavity cross-section is possible. The '918 patent also describes a microcavity plasma device formed from a semiconductor diode. A cavity is formed that extends through the depletion region of the reversed-biased diode and the surface of at least one of the semiconductor layers. The diodes are reverse-biased so as to ignite gas in the microcavity. The electric field is most intense in the depletion region of a reverse-biased diode. Unfortunately, switching and modulation of these devices requires substantial voltages (about 200 V) and electronics capable of switching such voltages are expensive.
Microplasma devices powered by a reverse-biased pn junction were also described in U.S. Pat. No. 6,815,891 issued on Nov. 9, 2004 and entitled, “Method and Apparatus for Exciting a Microdischarge.” For this invention, the gas within a channel extending through a semiconductor pn junction is excited by the electric field produced when the pn junction is reverse-biased. The microplasma thus produced is exposed to the semiconductor wall of the channel and plasma is produced in the channel in the vicinity of the pn junction.
Others have produced semiconductor structures that conduct electrons through space in a vacuum. Examples are described in U.S. Pat. No. 6,577,058 (the '058 patent) to Ossipov et al., and U.S. Pat. No. 4,683,399 (the '399 patent) granted to Soclof. In the '399 patent, a semiconductor device is disposed in a hermetically sealed container enclosing a vacuum. The device provides an emitter which emits electrons into vacuum and a collector to receive the electrons. The '058 patent discloses a cold electron emitter that also operates in vacuum. The emitter includes a junction that can control electron emission into the vacuum. Electron emitters such as those in the '399 and '058 patents can be used to produce displays, but require operation in a vacuum.